I like a window seat for the view so I prefer the 2-4-2 seating on a A330/340.
I flew BA to Canada last last year. The outward journey was on a B777. Nice plane and spacious looking but it doesn't feel that way when you're hemmed in by two other people. The journey back was on an old B767 which I wasn't looking forward to. However, the seats were new, the seat back video screen was huge and I swear there was more legroom. The 2-3-2 layout seemed an optimal combination of general roominess and easy accessibility.
Other factors like price, routing and frequent flier points might affect my booking decisions more but the seating layout in economy will also play a role. Of course, give me an upgrade on long haul and I'll be willing to fly any aircraft...